Loss of blood is a major cause of death in military combat and emergency situations in which the injured person is alone or medical assistance is not immediately available. The use of a tourniquet to stop blood loss from an injured arm or leg is a well-known technique for preventing death in these situations. Once the primary objective of preventing death due to blood loss is achieved, it is desirable to prevent further injury to the limb due to excessive pressure and time of tourniquet application. To minimize mechanical injury to the tissues under the tourniquet, the pressure applied by the tourniquet should be only slightly higher than that required to stop blood flow and the pressure should be applied evenly and uniformly around the limb beneath the tourniquet, without localized regions of very high or very low pressures. To help prevent gangrene and other complications related to the lack of arterial blood flow into the portion of the limb distal to the tourniquet, it is widely accepted that the tourniquet pressure should be released for a period of 5-10 minutes and then reapplied after each two hour period of stoppage of arterial blood flow, also called arterial blood flow occlusion. When more sophisticated care becomes available (such as emergency medical personnel arriving at the scene or evacuation to a field hospital), it is advantageous to have the emergency tourniquet compatible with more sophisticated pneumatic tourniquet systems (such as the pneumatic systems described by McEwen in U.S. Pat. No. 4,469,099) which allow precise control of tourniquet cuff pressure and application time.
Published US Army research (Calkins et al, xe2x80x98Evaluation of possible battlefield tourniquet systems for the far-forward settingxe2x80x99, Military Medicine Vol. 165, 5:379, May 2000) defines the need for a light, compact, yet rugged tourniquet for far-forward battlefield use. The victim must be able to apply the tourniquet to his or her own arm or leg and occlude blood flow using only their non-dominant hand. In the Calkins study, a variety of prior art pneumatic and non-pneumatic tourniquets and other non-pneumatic devices adapted for use as a tourniquet (such as ratcheting cargo straps) were tested and found to have disadvantages or to be ineffective in occluding arterial blood flow, particularly when self-applied. Calkins et al reviewed issued patents and found no suitable devices disclosed.
In U.S. Pat. No. 4,243,039, Aginsky discloses an emergency tourniquet consisting of a strap and ratchet-type tensioning device, including a tension indicating device and a pointer intended to be set by the user to indicate the time of tourniquet application. In the Calkins study a similar ratchet type devices did not successfully occlude arterial blood flow in all cases and the noisy operation, pinching of the skin, and questionable durability of these types of device was criticized. The pointer device disclosed by Aginsky in the ""039 patent requires the victim to set the pointers at the time of tightening the tourniquet and then monitor the current time using separate means to determine when to release the tourniquet. This is a disadvantage in the battlefield or emergency situation because the user, who may be injured and under extreme stress, must have a reliable separate means of measuring time, must remember to set the pointers immediately after tightening the tourniquet the limb, and must be alert enough to monitor the time throughout the maximum desirable period of continuous arterial occlusion.
There are many other non-pneumatic constricting devices (such as elastic and non-elastic straps) in the prior art. For example the emergency bandage described by Grau in U.S. Pat. No. 5,628,723 is intended to be wrapped tightly around the limb as a pressure dressing, but may be used as a tourniquet by using a windlass to twist the wrapped bandage and generate sufficient inward radial pressure on the limb to stop arterial blood flow. However the Calkins study showed that these types of devices were generally not capable of stopping arterial blood flow in the limb, particularly when self-applied by the victim. In U.S. Pat. No. 5,314,437, Holtsch describes a constricting device for body parts in which a non-inflating band encircles the body part. When the band is pulled tight, the resulting tension activates a rocker clamp which locks the band at a fixed circumference. Although this device may be easier to self-apply due to the automatic clamp, it is intended for venous occlusion only and it would be difficult or impossible for the victim to generate sufficient tension in the band to occlude arterial blood flow. In U.S. Pat. No. 6,149,666, Marsden describes a constricting strap and fastener device with a battery powered timer and alarm system activated by closure of the fasteners at one or more discrete circumferences. However this non-pneumatic device is a venous tourniquet to assist in various intravenous procedures and is not suitable for arterial occlusion.
Non-pneumatic strap type tourniquets such as those described above generate inward radial compression on the limb by being put into high levels of circumferential tension when wrapped around the limb. In ratcheting strap devices (such as that described by Aginsky in the ""039 patent) and other strap and buckle type devices (such as that described by Holtsch in the ""437 patent and the cargo strap device tested by Calkins), tension is generated by shortening the strap wrapped around the limb. As the pressure on the limb increases, the friction between the strap and the limb also increases, causing the underlying soft tissue to move with the strap as it is drawn tight. This tends to draw soft tissues underlying the strap into the ratchet or buckle device, pinching the soft tissue and creating a region of very high localized pressure which will cause unnecessary injury. This effect may also create high shearing stresses in the underlying soft tissues, increasing the probability of nerve and tissue injury. Friction between the strap and the limb may also create regions of low pressure by preventing tension from being distributed evenly in the strap around the entire limb circumference, and as a result arterial blood may still flow through these low pressure regions although overall strap tension is very high. In general, the uneven or non-uniform application of pressure around the limb resulting from the use of non-pneumatic strap type tourniquets leads to the need for unnecessarily high overall tourniquet pressures to reliably and predictably stop arterial blood flow, and this need for unnecessarily high pressure increases the probability of a range of unnecessary injuries to nerves, muscles and limb. Using a pressure transducer as described by McEwen in U.S. Pat. No. 4,869,265, the inventors of the current invention have found that pressure distribution under non-pneumatic strap type tourniquets is difficult to regulate and can vary significantly between different locations around the limb circumference and between the proximal and distal edges of the strap. In particular, pressures actually applied to the limb can be dangerously high in certain areas (such as the pinched areas described above) with corresponding increased risk of soft tissue and nerve damage. Areas of low pressure can allow arterial blood flow past the tourniquet and lead to higher overall strap tensions being used to maintain arterial occlusion. Furthermore, none of the non-pneumatic devices described above are compatible with typical operating room or field hospital tourniquet systems allowing precise control of tourniquet pressure.
Pneumatic tourniquet cuffs have been proven to be effective and safe devices for stopping arterial blood flow and are the standard of care in modern surgery. A pneumatic cuff was the only device tested that successfully stopped arterial blood flow in all trials in the Calkins study. When a pneumatic tourniquet cuff is in use, an inflatable bladder completely encircles the limb and is inflated, causing the bladder to expand and apply inward radial compression to the limb around the entire limb circumference. In contrast to the non-pneumatic devices described above, pneumatic tourniquets apply pressure to the limb that is very closely related to the inflation pressure of the cuff, and this pressure is applied evenly around the entire limb circumference. It is therefore easy to control the pressure applied to the limb by monitoring the cuff inflation pressure, and low pressure areas are minimized. Because the inward radial pressure on the limb is provided by the inflation pressure in the bladder rather than circumferential tension, the cuff does not need to be applied with great tension and the problems of pinching and shearing of the soft tissues (as described in the preceding paragraph) are minimized and self application is easier. A pneumatic tourniquet cuff must, however, be snugly applied around the limb and secured at a fixed circumference to be effective.
The pneumatic cuff tested in the Calkins study was similar to the overlapping occlusive cuffs for surgical use described by McEwen in U.S. Pat. Nos. 5,649,954 and 5,741,295. These cuffs consist of an inflatable bladder portion longer than the circumference of the largest limb expected to be occluded with the cuff, such that the bladder overlaps upon itself when wrapped around the limb. To help maintain an even pressure distribution around the limb and to reduce the likelihood of slippage of overlapping regions of the cuff along the limb, the amount of overlap in surgical tourniquet cuffs is generally limited to a range of roughly 1 to 5 inches, meaning that different cuff sizes are required to accommodate the arm and leg circumferences of different individuals. Overlapping pneumatic tourniquet cuffs are intended for use in the surgical setting where a source of compressed gas is available and the cuff is applied by a skilled technician. Typically the appropriate size of cuff is selected and wrapped around the limb and secured by hook and loop type fastening straps. The cuff is then inflated, and the full length of the bladder (both the portion contacting the limb and the overlapping portion) inflates. This type of cuff is undesirable in the battlefield or emergency situation because:
It is difficult to wrap these cuffs and close the fasteners with one hand (particularly on one""s own limb),
Hook and loop type fasteners can become unreliable when wet and fouled with dirt,
The inflated volume of these overlapping cuffs is always large enough for the largest limb in the recommended size range, even when the cuff is applied to the smallest limb in the range. This is a disadvantage when the user must inflate the cuff quickly with a manual pump, and
The limb size range of these overlapping cuffs is typically too narrow for a single cuff type to be applied to either an arm or a thigh, and so several different cuff sizes would have to be carried.
A non-overlapping tourniquet is described by McEwen in U.S. Pat. No. 4,770,175. This cuff has a sliding clamp that secures the cuff snugly around the limb before inflation, and the excess length of the bladder hangs loose from the clamp. The bladder is inflated from the end of the excess bladder portion, and the clamp therefore allows air inside the bladder to pass through from the excess bladder portion into the bladder portion encircling the limb such that the full length of the bladder inflates; the cuff will not function if the clamp seals the bladder into separate sections. The inflated bladder portions on both sides of the clamp prevent the bladder from sliding through the clamp and therefore help maintain a fixed bladder circumference around the limb. However the additional inflated volume of the excess bladder length is a disadvantage in military and emergency situations, as described above. Furthermore, the clamp described in the ""175 patent is intended to be applied by a skilled technician and is not adapted to single-handed operation; specifically the ends of the bladder are held in one hand and the clamp is slid down to the limb and closed using a second hand.
Pneumatic tourniquet cuffs require a source of pressurized gas to inflate the bladder, but the weight, bulk, and power requirements of surgical type pressure regulation and time monitoring systems (such as the pneumatic systems described by McEwen in U.S. Pat. No. 4,469,099) make them impractical for emergency self-use. Manual inflation means such as a hand pump or bulb (as shown with the overlapping pneumatic cuff tested by Calkins) is a practical alternative. However, even with manual inflation means, elapsed inflation time and cuff pressure should be monitored and indicated to the user to allow for minimization of the injuries and complications described in the opening paragraph. These monitoring and indicating functions ideally require minimal input from the user, who is likely under extreme stress while using the tourniquet.
There is no prior art pneumatic tourniquet for stopping arterial blood flow known to the inventors of the current invention which provides for self-application of the cuff with one hand, is suitable for a range of circumferences allowing application to the upper or lower limb, and inflates only in the region encircling the limb to which the cuff is applied. Furthermore there is no prior art pneumatic tourniquet cuff as described above known to the inventors of the current invention which also includes inflated time indication means automatically activated by manual pressurization of the tourniquet.